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Deflection of Ag-atoms in an inhomogeneous magnetic field

Kheswa, Bonginkosi Vincent (2011-12)

Thesis (MSc)--Stellenbosch University, 2011.

Thesis

ENGLISH ABSTRACT: In the current design of the high temperature gas cooled reactor, a small fraction of
coated fuel particles will be defective. Hence, 110Ag may be released from the fuel
spheres into the coolant gas (helium) and plate out on the cooler surfaces of the main
power system. This poses a radiation risk to operating personnel as well as general
public.
The objectives of this thesis were to design and construct an apparatus in which
silver-109 atoms may be produced and deflected in an inhomogeneous and
homogeneous magnetic field, compare experimental and theoretical results, and make
a recommendation based on the findings of this thesis to the idea of removing silver-110 atoms from the helium fluid by deflecting them with an inhomogeneous magnetic
field onto target plates situated on the inner perimeter of a helium pipe.
The experimental results for the deflection of the collimated Ag- atoms with the
round-hole collimators showed a deflection of 1.77° and 2.05° of the Ag- atoms due to
an inhomogeneous magnetic field when the target plate was positioned 13 and 30 mm
away from the magnet, respectively. These values were considerably greater than 0.01° and 0.02° that were calculated for the average velocity
of atoms, v = 500 m/s. The case where Ag- atoms were collimated with a pair of slits
and the target plate positioned 13mm away from the magnet showed the following:
An inhomogeneous magnetic field changes the rectangular shape of the beam to a
roughly elliptical shape. The beam of Ag- atoms was not split into two separate beams.
This was caused by the beam of Ag- atoms consisting of atoms travelling at different
speeds. The maximum deflection of Ag- atoms was 1.16° in the z direction and 1.12°
in the x direction. These values were also significantly greater than 0.01 mm calculated
at v = 500 m/s. This huge difference between the theoretical and experimental results
raised a conclusion that the size of each Ag deposit depended mostly on the exposure
time that was given to it. It was noticed that the beam of Ag- atoms was not split into
two separate beams, in both cases.
The conclusion was that the technique of removing Ag- atoms from the helium stream
by means of an inhomogeneous magnetic field may not be effective. This is due to the
inability of the inhomogeneous magnetic field to split the beam of Ag- atoms into two
separate beams in a vacuum of ~10-5 mbar. It would be even more difficult for an
inhomogeneous magnetic field to split the beam of Ag- atoms in helium, due to the
Ag- atoms having a shorter mean free path in helium compared to a vacuum.